Summary of work: Pharmacokinetic studies determined a plasma concentration of arecoline, a cholinergic agonist that improved memory in Alzheimer's disease (AD) patients and predicted an optimal dose in all subjects. Arecoline administration improved different cognitive functions at different doses. Verbal ability improved at low doses, whereas attention and visuospatial ability improved at higher doses. Administration of physostigmine, an inhibitor of brain acetylcholinesterase, also showed a modest improvement in verbal memory in most AD patients.